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This study was set to examine the fundamentals of solidification microstructure and room-temperature fracture toughness of different eutectic aluminum (Al) alloys strengthened by T-Al 6 Mg 11 Zn 11 and/or β-Al 3 Mg 2 intermetallic phases. The thermodynamic calculations for an Al-Mg-Zn ternary system assessed three alloy compositions of corresponding to α-Al/T, α-Al/β and α-Al/T/β eutectic compositions, respectively. The designed alloys were prepared by different cast process for changing the cooling rate in solidification. The Al-22.5Mg-23.5Zn and Al-35.5Mg-2Zn alloys exhibited a number of fibrous α phase surrounded by of T-phase and β-phase matrix, respectively. The morphologies of eutectic microstructures were refined by high cooling rate in solidification. The three-phase microstructure of α, T and β phases was often observed in slowly solidified Al-34.5Mg-5Zn alloy, whereas only the α/β two-phase eutectic microstructure was observed in the rapidly solidified alloy sample. The indentation fracture method using Vickers indentation test was applied to measure the room-temperature fracture toughness of the experimental alloys prepared by mold-casting. The α/β twophase eutectic alloys exhibited a low fracture toughness of 1.1 MPa•m 0.5 in comparison with the α/T two-phase eutectic alloy. The lower fracture toughness would be responsible for the brittleness of β-phase matrix in the α/β twophase eutectic alloys.

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast AlFe alloys, we have fabricated various AlFe-based alloys with compositions of Al1%Fe, Al1%Fe1%Mn, Al1%Fe1%Cu, and Al1%Fe 1%Cu1%Mn (mol%) solidified at different cooling rates (0.3 K•s ¹1 and 145 K•s ¹1 ). In the Al1%Fe binary alloy, the coarsened ª-Al 13 Fe 4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K•s ¹1 ), whereas the cast sample (145 K•s ¹1 ) exhibited several elongated ¡ phases surrounded by fine ¡/Al 6 Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al 1%Fe1%Cu alloy, whereas the Al 23 CuFe 4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al 1%Fe1%Mn alloy, the Al 6 (Fe, Mn) phase was formed regardless of the cooling rate. Finer ¡/Al 6 (Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al1%Fe1%Cu1%Mn alloy as well.Compression tests for cast alloy specimens revealed that the Al1%Fe1%Cu1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast AlFe alloys.